This invention relates to a pivot bearing, particularly, though not exclusively, for a vehicle trailing arm suspension.
Pivot bearings in a vehicle trailing arm suspension are subjected, in use, to forces in the vertical, horizontal, axial and torsional directions. It is desirable that the bearings be able to absorb these forces, including shock and out of phase wheel loading, and have a prolonged useful life.
Conventionally, pivot bearings for vehicle trailing arm suspension systems include a housing containing a generally cylindrical bush on a rigid axial sleeve in which a pivot of a trailing arm is located. Whilst being essentially stiff, the bush has some resilience intended to absorb vertical, horizontal and torsional forces, particularly roll induced forces and out of phase wheel loads. Usually, the bush is made of a rubber material. Bushes have been made solid and with the same level of stiffness/resilience all around the axial sleeve. This limits the effectiveness of the bush because the stiffness/resilience requirements at different angularly positioned parts of the bush around the pivot may vary appreciably in practice according to the direction in which loads are exerted on the bush in use. If the bush is heavily loaded in use, it will usually have a high level of stiffness which makes it too stiff for satisfactory absorption of loads. Alternatively, if the bush is made with a compromised level of stiffness/resilience for the range of loads exerted on it in use in different directions, its performance is clearly limited.
In order to vary the stiffness of the bush for different levels of forces acting on the pivot bearing from different directions in use, bushes have been made with voids, usually arcuate, above and below the axial sleeve. This softens the rate of the bush under general vertical loading whilst retaining greater stiffness in the generally longitudinal direction of the vehicle for compliance under roll and out of phase wheel loading. However, the stiffness provided in the generally longitudinal direction is limited and may be insufficient to cope satisfactorily with increasing loading conditions under which some vehicles are expected to operate.
According to a first aspect of the present inventions, a pivot bearing includes a housing which attaches the pivot bearing to a support means, a resilient generally cylindrical bush contained in the housing, and a rigid axial sleeve secured in the bush at which the pivot bearing is located for use. Voids are formed in first portions of the bush. When the pivot bearing is fitted for use, the voids are disposed above and below the axial sleeve. The pivot bearing includes stiffening elements made of material stiffer than that of the bush. The stiffening elements are contained in second portions of the bush and extend between the first portions at opposite sides of the axial sleeve.
The stiffening elements increase the stiffness of the bush in generally horizontal directions for improved vehicle dynamics and reduced vibration when the pivot bearing is in use.
The stiffening elements are rigid. They can be made of metal such as steel, or of a suitable plastics material. Preferably, the stiffening elements are securely retained, by bonding, to the bush. The stiffening elements can be of a plate or leaf form. The stiffening elements extend arcuately in the second portions about the sleeve. They can also take other forms. There can be a single stiffening element at each side of the sleeve, or there may be more than one stiffening element. Each stiffening element extends through the axial length of the bush and can project from the opposite ends of the bush.
Preferably, the bush is formed by molding. The voids are formed in the bush as it is molded. The stiffening elements are incorporated into the bush as it is molded, and the material of the bush is then bonded to the stiffening elements in the course of the molding process.
The voids extend arcuately, or generally arcuately, in the first portions of the bush about the sleeve. They can extend through the axial thickness of the bush, or partially through the thickness. The voids can extend into the bush from opposite end faces of the bush. In this latter arrangement similar, directly opposed, voids extend towards one another from the opposite end faces, but are separated by a central solid region of the bush.
Preferably, as viewed from each of the opposite ends of the bush, in the position of use of the pivot bearing, there is one elongated void above and one below the sleeve. Each void extends for a longer distance about the sleeve than the external diameter of the sleeve. Opposite ends of each void extend through and beyond notional parallel planes extending vertically tangentially of diametrically opposite parts of the external circumference of the sleeve. This increases the flexibility of the bush under generally vertical loading. Preferably, the ends of the voids are also enlarged, assisting in reducing stresses in the material of the bush at the ends of voids and facilitating compression of the bush under vertical loading. The annular width of the end regions of the voids can be increased and enlarged. In another form, the ends of the voids are enlarged by shaping them into two or more lobes, fingers or comparable projections running from the main bodies of the voids. At least one such projection at each end of a void extends inwardly towards the sleeve. In a preferred form, the ends of the voids are turned inwardly towards the sleeve to provide the enlargements. The ends of the voids can be turned inwardly at an angle, preferably substantially radially of the sleeve. Each end of the voids can also taper generally triangularly towards the sleeve.
The bush can have an interference fit in the housing. Alternatively, it can be bonded and/or molded into the housing.
In a preferred embodiment, the bush is formed, as by molding, separately from the housing and is then compressed into and bonded in the housing. The bush is fixed on the sleeve before insertion into the housing. The voids of the uncompressed bush are open so that the opposite longitudinal sides of the elongated voids extending above and below the sleeve are spaced apart. The ends of the voids are turned inwardly towards the sleeve in the manner described above and taper generally triangularly towards the sleeve. Upon insertion of the bush into the housing, and its radial compression thereby, the compression of the first portions containing the voids causes the opposite longitudinal sides of the voids to close together. In the assembled pivot bearing, therefore, the voids are substantially closed; only the inturned ends of the voids may remain open, through to a lesser extent than in the uncompressed state of the bush. Although the voids are closed, the first portions remain relatively compressible, thereby affording substantial compliance in the bush under loading in the vertical, and generally vertical, directions.
By contrast, the compression of the bush at the second portions resulting from its insertion into the housing, in combination with the stiffening afforded by the stiffening elements, leaves the second portions substantially stiffened against further compression under horizontal, and generally horizontal, loading on the bush when it is in use.
The stiffening elements, at least in the plate or leaf form, extend into opposite ends of the voids. When the ends of the voids are enlarged into lobes, fingers or comparable projections, as described, the stiffening elements preferably extend into the voids between adjacent projections. In the preferred form of the voids having the inwardly turned ends, the material of the bush is radiused into the ends of the voids at the stiffening elements where the stiffening elements break into the voids. These arrangements reinforce the bush where stresses are concentrated under vertical, and generally vertical, loading and help to prevent separation of the material of the bush from the stiffening elements adjacent the voids.
The bush can be bonded to the sleeve. When the bush is molded, it can be bonded onto the sleeve as it is molded. The sleeve can protrude from the opposite ends faces of the bush.
In one example, the sleeve is axially longer than the housing for compliance of the bush under axial and tilting loading. The sleeve projects symmetrically from the opposite axial ends of the housing. Preferably, the bush is shaped to correspond substantially in axial length to the length of the sleeve at its internal diameter and to have its ends inclined away from the sleeve so that the axial length of the bush reduces towards its external diameter. This allows for tilting of the bush relative to the sleeve and bulging of the ends under loading.
In one embodiment, a pivot bearing is made to be used in a vehicle trailing arm and its attachment to a supporting part of the vehicle. The pivot bearing is designed to withstand horizontal, vertical, axial and torsional loading when in use. The housing of the pivot bearing is cylindrical and co-axial with the sleeve. The bush is bonded onto the rigid axial sleeve and securely retained in the housing. Both the sleeve and housing are made of metal, for example steel. The bush has a cylindrical body with frusto-conical, or convex, end faces. The sleeve is longer than the housing and projects from the end faces of the body. The body is made of a rubber, polyurethane, or comparable, flexible material. Generally arcuately extending elongated voids are formed in first portions of the body. When the pivot bearing is fitted for use, the voids are above and below the sleeve, the voids opening through the end faces of the body. The voids are longer arcuately than the external diameter of the sleeve and have inwardly turned end portions which taper triangularly, generally radially, towards the sleeve. Stiffening elements extend through the second portions of the body adjacent diametrically opposed sides of the sleeve. There is one stiffening element at each side of the sleeve. The stiffening elements are made of metal, for example steel, and are of a plate or leaf form arcuately curved concentrically about the sleeve. The stiffening elements are shorter than the sleeve, extend through the full axial length of the body, and protrude from the opposite end faces of the body. Each stiffening element projects into the adjacent end portions of the voids.
The housing is fixed to the trailing arm for use of the pivot bearing such that the central longitudinal axis of the sleeve extends horizontally transversely of the arm. A pivot pin is located in the sleeve and is supported by opposed limbs of a mounting which straddles the pivot bearing and is fixed to the supporting part of the vehicle. The protruding ends of the sleeve abut, or bear on, thrust washers which abut opposed, inner surfaces of the respective limbs of the mounting. In use of the suspension system, generally vertical and horizontal loadings imposed on the pivot bearing by relative movement between the pivot pin and trailing arm are accommodated respectively by the voided first portions of the bush and the second portions stiffened by the stiffening elements. The body of the bush is able to sustain axial, torsional and tilting loading on the bush.
The pivot bearing can be included as original equipment on a trailing arm of a vehicle trailing arm suspension system.
Thus, according to a second aspect of the present invention, there is provided vehicle trailing arm including a pivot bearing in accordance with the first aspect of the invention herein set forth, the housing of the pivot bearing begin fixed with respect to the trailing arm.
According to a third aspect of the present invention, there is provided a vehicle trailing arm suspension system including at least one trailing arm in accordance with the foregoing second aspect of the invention.